Correlation methods for determining the strength of the linear relationship between two or more variables are among the most widely applied statistical techniques. One of the most common areas of application is in geophysical exploration where it is desirable to perform a correlation operation on geophysical logs. The desirability of performing such a correlation operation is the determination of the degree of match, or similarity, of portions of the logs. The correlation function produced by correlating the two logs has a magnitude indicative of the degree of match, or similarity, of sections of the logs. Correlation is a well known statistical operation as generally described in Seismic Exploration Fundamentals, by J. A. Coffen, the Petroleum Publishing Co., Tulsa, Okla., 1978, pages 115-118 and in Encyclopedia of Statistical Sciences, Vol. 2, John Wiley & Sons, N.Y., 1982, pages 193-204. One good example is the determination of the dip of subsurface beds from well logs. In this case, correlation of the logs produced in a pair of spaced-apart boreholes produces a function having a maximum which occurs at a depth difference which is indicative of the dip of the subsurface layers between the two boreholes. Such an example is shown in U.S. Pat. No. 3,304,535 to P. L. Lawrence.
Another example of the use of correlation techniques in geophysical prospecting is the correlation of the various components of a dipmeter log from a single borehole to determine the depth displacements between such components. These depth displacements will depend on the dip magnitude and direction of the formation bedding surfaces.
Correlation has been successfully applied in the geophysical art to both seismograms and various types of well logs.
Examples of such correlation operations on dipmeter logs are described in "Automatic Computation of Dipmeter Logs Digitally Recorded on Magnetic Tapes" by Moran, Coufleau, Miller and Timmons, Petroleum Transactions, July, 1962, Pages 771-782; Dipmeter Interpretation, Schlumberger Limited, N.Y. 1986, pages 1-12; and Cluster--A Method For Selecting The Most Probable Dip Results From Dipmeter Survey, by Hepp and Dumestre, Society of Petroleum Engineers of AIME, Dallas, Tex. 1975, SPE 5543, Pages 1-16.